In Christianity, postmillennialism is a viewpoint on the end times, which contends that the Second Coming of Jesus Christ will occur after the millennial period that is mentioned in the book of Revelation (cf. 20:1-6). In this view, the number 1,000 isn't to be understood literally, but as just a long period of time. Postmillennialism is often compared and contrasted with premillennialism and amillennialism.
Postmillennialists believe that the Kingdom of God that exists now will be extended throughout the world by means of the Church's proclamation of the gospel. At the end of the millennial period, however long that lasts, postmillennialists believe Christ will return, at which time the resurrections and judgments will occur, followed by the eternal state.
Postmillennialists interpret certain passages of Scripture as teachings that there will be a time of peace and prosperity on the earth. For instance, Psalm 22:27 reads, "All the ends of the earth will remember and turn to the Lord and all the families of the nations will bow down before Him." To the postmillennialist, this verse teaches that there will be no supernatural event (such as "the rapture" as held by premillennialism), except for the proclamation of the gospel, that will inaugurate the millennial period.
Postmillennialism can be graphed in the follow way:
Christ Second Coming __|___|__ Church Age >>>>>>>>>> The Millennium The Eternal State
An important passage to postmillennial beliefs is Isaiah 2:2-4.
In the last days the mountain of the Lord's temple will be established as chief among the mountains; it will be raised above the hills, and all the nations will stream to it. Many people will come and say, “Come, let us go up to the mountains of the Lord, to the house of the God of Jacob. He will teach us His ways, so we may walk in His paths.” The law will go out from Zion, the word of the Lord from Jerusalem. He will judge between the nations and settle disputes for many people. They will beat their swords into plowshares and their spears into pruning hooks. Nation will not take up sword against nation, nor will they train for war anymore.
In this passage, advocates point out that terminology concerning the end of the world (i.e. "in the last days") is the context for the description of nations at peace with one another (i.e. "nation will not take up sword against nation"). This description is different than the premillennial understanding of the end of the world, which is characterized by warfare and other atrocities.
It's also emphasized that there is no mention of preceding events, even supernatural ones, such as the rapture, as advocates of premillennialism believe there will be. To the postmillennialist, preaching the gospel results in a peaceful planet under God's sovereignty.
The establishment of the millennial period includes two phases, according to postmillennialism. The first phase is the incarnation, death, and resurrection of Christ. The second phase is believers preaching the incarnation, death, and resurrection of Christ. Postmillennialist Kenneth L. Gentry Jr. writes:
The massive influence of Christ's reconciling death will operate in history through the age-long drawing of all men, resulting in the world-as-a-system returning to God. He will not accomplish this catastrophically by external political imposition, but gradually by internal personal transformation. Redemptively transformed people generate a righteously transformed world. God's gracious drawing finally results in a massive, systemic conversion of the vast majority of humankind. This universal drawing leads to a redeemed world.